I believe we should use Mirek's command receiver on L band as adapted 
for our purposes.  If we want a redundant one for any reason,  we do 
that one on 70cm.  The command receiver should feed the IHU-3 SDR for 
any normal commanding and any reset vector decoder we choose to enable.

The issue is straightforward.   Any module that needs a heat sink will 
have been designed to be kept cool when the spacecraft is receiving a 
large thermal input from the sun.  When this thermal input is removed,  
the same radiation cooling that was keeping the module cool will  
continue to operate irrespective of the solar input.  That module will 
get cold over time.  If the bottom temperature stops the unit from 
operating properly and it is a command receiver,  this is not a good 
thing.   I believe we should have dedicated command receivers anyway and 
these to do not need 80 dB of dynamic range and can be made narrow 
band.  Our solar eclipse pattern has been given a preliminary analysis 
for the proposed orbit and we will be subjected to eclipses of 
insufficient duration to cause us severe thermal problems but what 
thermal issues there are need to be understood and this is what Dick is 
warning us about.  This analysis of the eclipse pattern was also the 
basis of my analysis that it would take well over a decade to subject 
any Li-ion battery to sufficient cycles to worry about.

Bob
N4HY


John B. Stephensen wrote:
  

The SAW filters work down to -35 C and the ICs to -40 C so its not too 
far off. It's easy to use a lower power RF amplifier and mixer which 
will lower the input intercept. Right now, the receiver is designed to 
tolerate direct hits from PAVE PAWS at any two frequencies outside the 
IF passband. As the input intecept is lowered, the percentage of 
pulses that cause interference increases, but the receiver won't go 
completely deaf as was reported on earlier satelites.
 
73,
 
John
KD6OZH

    ----- Original Message -----
    *From:* Dick Jansson-rr <mailto:[email protected]>
    *To:* AMSAT Eagle <mailto:[email protected]>
    *Sent:* Wednesday, October 11, 2006 17:51 UTC
    *Subject:* [eagle] Module Temperatures

    Last evening I tried to convey the concept that the
    critical-command modules needed to be of low-power design to
    insure their operability during the occasional rather lengthy
    eclipse cooling of the spacecraft. My message apparently did not
    sink in. John reports that his design of such a U band receiver
    would be dissipating some 3.5W due to its bullet-proof nature
    against 3rd-order IM products needed for protection on the U band.
     
    If we go forward with such a module of that nature, it will need
    to have thermal control tapes on it to provide a mean emittance of
    about e=0.45. In a 3 hour eclipse we can expect to see spaceframe
    temperatures down to -100°C (173K) or lower. With such an
    environment John's module would be expected to see temperatures
    down to at least -44°C, which is a bit frosty for electronics that
    are expected to provide the critical services of commanding the
    spacecraft. Such operating temperatures are not felt to be
    advisable for that service.
     
    If John's module were of the 1W category, temperatures of the
    receiver could be expected to be in the range of -15°C to -20°C
    which would be more operable for the service.
     
    The above numbers are, of course, based on estimates which will be
    confirmed after we have the new spaceframe fully designed and
    analyzed. The "warmer" temperatures of the lower power modules are
    those that have been experienced and measured by telemetry from
    AO-10 and AO-13. These projections are thus based on 25 years of
    experience in these design concepts.
     
    /Dick Jansson/
    _---------------------------_
    [email protected] <mailto:[email protected]>
    _---------------------------_

     

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